The present invention relates to a liquid crystal displaying apparatus for televisions, projectors and the like. Particularly, this invention relates to a displaying apparatus using an active matrix transmission- or reflection-type liquid crystal display device, and a method of displaying an image by the display device.
Recently, a color liquid crystal displaying apparatus has widely been used as a display for televisions, personal computers, projectors with a large screen for projecting moving pictures, and so on. Particularly, a transmission-type liquid crystal display device is applied to the televisions and personal computers. On the other hand, a reflection-type liquid crystal display device is applied to the projectors. The liquid crystal display devices are combined with a color filter to achieve a precise and distortion-free image.
Generally, the active matrix driving method is employed for a liquid crystal displaying apparatus as shown in FIG. 1. The apparatus shown in FIG. 1 includes a signal processor 1, a digital-to-analog (D/A) converter 2, an amplifier (AMP) 3, an inverter 4, an analog switch 5, a switch controller 6, an offset voltage applier 7 and a liquid crystal display device (LCD) 8.
A video signal supplied to the apparatus is subjected to digital processing by the signal processor 1 and converted into an analog signal by the D/A converter 2. The analog video signal is amplified by the amplifier 3 and inverted by the inverter 4. Either the amplified signal "a" or inverted signal "b" is selected for each field period by the switch 5 under the control of the switch controller 6. The selected signal "c" is clamped at a level by the offset voltage applier 7 and supplied to the liquid crystal display device 8.
In the apparatus shown in FIG. 1, the amplifier 3, inverter 4, switch 5 and offset voltage applier 7 are constituted by complex analog circuitry. Particularly, the offset voltage applier 7 is constituted by a damper and a complex buffer with high input impedance.
Concerning symmetry in the non-inverted video signal "a" and the inverted signal "b" in FIG. 1, highly precise gain, frequency characteristic, phase characteristic, and an offset amount are required. Those requirements are however difficult to meet by the complex circuitry, and an unevenness often occurs in the characteristics of the liquid crystal displaying apparatuses.
Furthermore, transfer of a polyphase video signal requires signal processing circuitry for each phase signal. A vertical stripe pattern noise would occur if the polyphase signal exhibits uneven characteristics. This results in an image of extremely low quality.
Accordingly, the conventional apparatus requires highly precise circuit components for securing the display precision and quality of the image. And, the analog circuit components must be adjusted accurately. These requirements results in a high manufacturing cost.
Particularly, for high-vision, the liquid crystal displaying apparatus must process the polyphase signal of eight or more phases. This results in a bulk analog circuitry.